1. Field of the Invention
The present invention relates to random number generating devices.
2. Description of the Related Art
It is known that random numbers are used as the ID (identification number) of a communication device such as an IC card or a contactless communication device. In such a case where random numbers are used as an ID, the random numbers are required to be highly irregular. In order to meet such a requirement, there is a known technique in which a stabilized power supply for supplying a constant output voltage to a load circuit is used, such that random numbers are generated by using a control signal that is generated by amplifying a variation of the output voltage from a reference voltage (e.g., Japanese Laid-Open Patent Application Publication No. 2007-122560).
FIG. 17 is a circuit diagram showing a configuration of a conventional random number generating device. As shown in FIG. 17, such a random number generating device as disclosed in Japanese Laid-Open Patent Application Publication No. 2007-122560 includes: a regulator 900; a voltage controlled oscillator (VCO) 930; and a random number generator 940. In order to supply a constant output voltage Vout as power supply for a load circuit 920, the regulator 900 amplifies a difference between a reference voltage Vref and a feedback voltage S93 by means of an amplifier 91, thereby generating a control voltage S91. Based on the control voltage S91, the output voltage Vout is adjusted. The VCO 930 outputs an output signal CLK whose oscillation frequency has been varied in accordance with variation in the voltage level of the control voltage S91. The random number generator 940 generates pseudorandom numbers based on the output signal CLK from the VCO 930. Accordingly, the pseudorandom numbers generated by the random number generator 940 vary in accordance with the oscillation frequency of the VCO 930 (i.e., vary in accordance with the control voltage S91 of the regulator 900). Therefore, the random number generator 940 can generate highly irregular random numbers, so long as the control voltage S91 varies constantly.
Also, Japanese Laid-Open Patent Application Publication No. H10-340183 discloses a configuration for generating pseudorandom numbers varying in accordance with variation in the voltage level of a control voltage inputted to a control terminal of a VCO.